The distal end has been figured by Prof. Owen in the British Fossil Mammals, p. 545; in Dixon's Geology of Sussex, Pl. XXIX. fig. 12; Cret. Reptiles, Pl. XXXII. figs. 4 and 5, First Supt. Pl. IV, fig. 9-11, and other places, and fully described. It closely resembles the distal end of a bird's tibia; and consists of a pulley-shaped end set obliquely on to the compressed shaft, which just above the junction is reniform in section, owing to the development of a median rounded ridge on the same inner side of the bone which bears the median ridge at the proximal end, while on the opposite side there is a corresponding median depression which does not extend far proximally. In this depression is an oval pneumatic foramen; on the right of the median ridge of the other side, but placed more distally, is another pneumatic foramen. The median ridge has sometimes a slight furrow on each side. It terminates proximally in strong muscular insertions, which extend round the right side of the bone; and distally, becoming more elevated and rounded, it curves obliquely to the rights and forming one of the sides of the pulley, passes round the base as three quarters of a spiral, the termination extending laterally beyond the shaft. On this side of the bone, distal to the median depression, arises another ridge strong and well rounded, which is directed to the right, similarly passes round the base as a spiral, and forms the other side of the pulley. It is not so prominent as the border previously described. While the spirals approximate at their origin, they become widely separated at the base, making the articulation wider than the shaft. In No. 31 the three inches of the shaft which remain show both pairs of its sides sub-parallel; the widest measures nearly an inch; the base of the articulation is less than a quarter of an inch wider.
Limited to the base, between the two outer ridges of the pulley, is a short median ridge slightly developed; so as to flatten the middle of the concavity between the ridges, and divide it into two grooves. The degree to which the middle ridge is developed varies in different species. In No. 30, the smallest pterodactyle, remarkable for a long wing-metacarpal bone, it is not to be detected. The exterior sides of the trochlear articulation are broad, flattened, and a little concave.
There is some variation in the way in which the shaft is set on the trochlear end. It being often in the middle, but not unfrequently inclined more to one side than to the other.
The metacarpus finds no close parallel among living animals. The thread-like metacarpal bones suggest the condition of the hind-foot in the Kangaroo. The predominant metacarpal suggests the ruminants. But the nearest approximation is found among birds where the bone for the middle finger is large and the bone for the third finger is slender. This may be observed (among other examples) in the Penguin and the Swan. But here the parallel ends. The proximal end in Birds, we have already seen to be hidden by the anchylosed distal row of the carpus, and the distal end though often convex from side to side never presents the trochlear joint of the Pterodactyle. Consequently so far as regards the form of the articular ends the resemblance is closer with Reptiles and clawed Mammals than with Birds. In Birds the small metacarpal is usually of similar length with the large one as is the case with Pterodactyles.
| Case. | Comp. | Tablet. | Specimen. |
| J | b | 6 | 1—10 |
FIRST PHALANGE.
[Pl. 7.]
No perfect specimen of the first phalange has been found in the Cambridge Greensand. Ten bones are mounted to illustrate it, all of them less perfect than others in the series of associated bones. No. 1 shows the heel of the proximal end; Nos. 9 and 10 are portions of the proximal articulation from which the epiphysis which forms the articular heel-part seen in No. 1 has come away. Nos. 2 to 8 are the distal articular ends of first phalanges. It is improbable that any of them belong to the second phalange, since they agree in form, and show muscular attachments which correspond.
Prof. Owen has figured the shaft of a fine example of this bone in Dixon's Geology of Sussex, Pl. XXXIX. fig. 11. A good proximal end is shown in Pl. XXXII. fig. 2, of Prof. Owen's monograph of the Cretaceous Reptilia, but the figure appears to have been previously given in Pl. XXIV. fig. 2 of the same monograph. By far the grandest specimens are drawn in Pl. XXX. Prof. Owen names these wing bones. In the "Literature of English Pterodactyles" the loss of the proximal epiphysis from the specimen represented in Prof Owen's fig. 1 and 2 led me to interpret the bone as an ulna. Figs. 1 to 4 represent the proximal ends and greater portions of the shafts of first phalanges. The lower bone in fig. 5 is neither radius nor ulna, as stated in the text of the Cretaceous Reptilia, but the shaft and distal end of a first phalange; the upper bone being the second phalange.
The Proximal End.
The straight shaft throughout its length is triangular in section. One side of the bone is gently convex; this may be named for convenience the outside. The two parts which make up the other side are inclined, and have the angle in which they meet rounded; one part looks upward and inward, the other downward and inward. Towards the proximal end the bone widens and thickens, and the moiety of the inner side which is away from the heel becomes cleft, and has the sides of the depression rounded to form a large pneumatic foramen. The articular surface looks upward and a little outward on the side of the pneumatic foramen. It consists of two semicircular concave grooves, separated by an intervening low convexity. The outer of these grooves extends from the margin of the extreme proximal point of the heel to the widest point of the bone; the other groove more deeply concave, is a third shorter, extending from inside the pneumatic foramen to the heel. Here both grooves converge, terminating in a point, exterior to which a little distally is a hemispherical mammilate eminence. On the distal side of the eminence there is a depression so as to make the angle behind the heel almost hemispherically rounded. This articulation fits on to the distal articulation of the wing-metacarpal.